The specification of U.S. Pat. No. 3,759,683 describes a "Process for the Manufacture of Multi-Component Substances" for the preparation of oxide glasses and ceramics. This process is an example of what is commonly known as the sol-gel process. In the conventional sol-gel process an alcoholic solution of a metal alkoxide or mixture of metal alkoxides is hydrolyzed under controlled conditions to form a sol which may be molded or used as a coating then cured to form a gel. Depending upon the application, a coating may be applied by dipping, spin coating, or any other suitable technique. Subsequently drying and heat treatment is then required to form a densified coating or monolith. While the treatment temperatures necessary are substantially below those required by conventional sintering or melt processing the temperatures needed are still substantially greater than can be withstood by many substrates. Thus there are considerable advantages to be obtained if sol-gel thin films and coatings can be cured to high density at temperatures approaching ambient. Sol-gel thin films have potential as diffusion and oxidation barriers, dielectric films, and scratch-resistant coatings. For microelectronic applications, sol-gel derived silicon dioxide and silicon-oxynitride thin films are attractive for passivation coatings, interlayer dielectrics and field and gate oxides, particularly for III-V semiconductors such as Ga-As. Developments in this area have been impeded however, because the temperatures required to densify the sol-gel are too high to maintain the integrity of the substrate in many situations. A low-temperature curing process would also offer advantages where it is desired to coat metals with a low melting temperature such as aluminum where the melting temperature of the metal is below that required to densify materials such as silicon dioxide.
Low pressure gas discharges or plasmas are known to effect changes in materials which normally occur only at high temperatures, this is because the molecules and atoms in the gas become excited and attain high energies in the electric discharge. When the atoms and molecules come into contact with a solid surface the result can be to activate the surface.
Other related U.S. Pat. Nos. include: 4,521,441 by Flowers where a film on a semiconductor substrate is treated in a plasma environment with about 10% oxygen (oxygen plasma). The film is a dopant material, including a glass former and a suitable solvent. The plasma treatment temperature is 150.degree. C.-400.degree. C. while the diffusion temperature is 850.degree. C.-1200.degree. C.; 4,472,512 to Lane shows a process for removing retained water in a sol-gel process by contacting the material with a gas and an organic compound; 4,429,051 to Davidge discloses a high temperature process for heating a sol-gel material and is only of general interest; 4,220,461 to Samanta shows a low temperature process for depositing a glass film by diffusion through a barrier between a first and second solution however final consolidation is done at a high temperature (about 1450.degree. C.) to form a consolidated nonporous glass; 4,170,663 to Hahn et al reveals a process in which a hard, mar-resistant, abrasive resistant coating is cured by ionizing radiation in an atmosphere containing a cure inhibiting amount of oxygen, in additicnal stages it is exposed to ultraviolet light and ionizing radiation; and finally 4,125,644 to Ketley et al discloses a process in which a protective coating is provided to a fiber optic material, subsequently exposing the material to ionizing radiation or ultraviolet radiation to cure the coating. The protective coating is a photopolymer.
It is therefore, the object of this invention to provide a method of curing and densifying sol-gel thin films at significantly lower temperatures than are possible using known techniques.
It is another object of the invention to provide a method of doping sol-gel thin films with foreign anions under the low temperature curing conditions.